An operator is something that takes one or more values (or
expressions, in programming jargon) and yields another value (so that the
construction itself becomes an expression).

Operators can be grouped according to the number of values they take. Unary
operators take only one value, for example ! (the
logical not operator) or
++ (the
increment operator).
Binary operators take two values, such as the familiar
arithmetical operators+ (plus) and - (minus), and the
majority of PHP operators fall into this category. Finally, there is a
single ternary
operator, ? :, which takes three values; this is
usually referred to simply as "the ternary operator" (although it could
perhaps more properly be called the conditional operator).

A full list of PHP operators follows in the section
Operator Precedence.
This also explains operator Presedence and Associativity, which govern
exactly how expressions containing several different operators are
evaluated.